This invention pertains to an improvement in the invention described in application Ser. No. 08/354,409, filed Dec. 24, 1994, and in particular in producing microcapsules containing biologically active compounds and further containing a suspended ultraviolet protectant agent.
As pointed out in application Ser. No. 08/354,409, while various types of microencapsulation techniques have been used to prepare microcapsules of biologically active compounds for pesticidal use, no satisfactory techniques to produce a microcapsule containing a solid biologically active pesticide suspended in a liquid had previously been known. There were several reasons for this, particularly the following difficulties:
1. It is necessary to produce a stable suspension of the biologically active solid in a water-immiscible liquid. If dispersants or surfactants are used, they must not interfere with further processes of dispersion used in making the microcapsules.
2. The suspension of the solid must be dispersed in water to produce stable well-dispersed droplets, preferably very small droplets of an organic-phase suspension dispersed in water. This requires high shear forces which would tend to break down the droplets and/or release the solid from suspension.
3. The presence of one or more surfactants can make the dispersed droplet system unstable and produce phase inversion.
4. The suspended solid is liable to migrate to the aqueous phase, particularly when emulsifying surfactants are used.
Application 08/354,409 describes techniques for producing microencapsulated formulations of a solid biologically active compound suspended in a liquid. The product is produced by essentially a three-step process. In the first step, the solid biologically active material is produced with a required particle size, for example by a milling process. In the second step, the solid biologically active compound is suspended in an organic liquid, preferably one which is a poor solvent for the solid and which is immiscible with water. The liquid, however, must be polar enough to dissolve the prepolymers used in the microencapsulation process. Alternatively, the solid may be first suspended in a liquid and then milled. In the third step, a physical dispersion of this water immiscible phase in an aqueous phase is prepared.
Some biologically active materials are adversely affected by ultraviolet or actinic light; even when they are microencapsulated, the active material in the capsule may still become degraded in the presence of light. A number of techniques have been proposed to provide ultraviolet light protection to microencapsulated materials. For example, Ignoffo et al., J. Economic Entomology, 64, 850 (1971) discloses use of cellulose, carbon, aluminum powder and aluminum oxide in protecting encapsulated virus samples from ultraviolet radiation. The authors do not describe the process by which the microcapsules were prepared. U.S. Pat. No. 3,541,203 describes the use of carbon black and other ultraviolet absorbers such as metal flakes, metal oxide particles, metal sulfides and other commonly used pigments to provide ultraviolet protection to a virus contained within a polymeric matrix. U.S. Pat. Nos. 4,844,896 and 4,948,586 disclose the use of a number of organic dyes and other sunscreening agents such as benzophenone, PABA and benzil (or mixtures thereof) for protection of encapsulated viruses. U.S. Pat. No. 4,328,203 discloses production of a microencapsulated pathogenic viral, bacterial or fungal material in a coacervate microbead comprised of a nucleic acid and a proteinaceous material, in which the microbead structure itself is a UV protectant. Finally, PCT application WO92/19102 discloses another type of microcapsule in which the encapsulating agent itself, this time lignin, also serves as the sunscreen.